The invention relates generally to a continuous casting mold.
More particularly, the invention relates to a mold for the continuous casting of beam blanks.
In the steel industry, the term "beam blank" denotes a semifinished product having a dogbone-shaped cross section. A beam blank is converted from a semifinished product to a finished product by rolling. The finished product is an I-beam.
It is known to produce beam blanks by continuously casting a heat of steel into a continuous casting mold having a dogbone-shaped cross section. Continuous casting has the advantage that a series of beam blanks may be formed from the heat in a continuous operation. This enables energy savings to be achieved and also improves production.
A mold for the continuous casting of beam blanks typically has a central casting passage which is bounded by a pair of parallel walls and is designed to form the web of a beam blank. On either side of the central casting passage is a second casting passage which widens in a direction away from the central casting passage. These second or expanding casting passages are designed to form the inner flanges of a beam blank. Each of the expanding casting passages merges into a generally rectangular terminal casting passage designed to form the outer flange of a beam blank.
In current rolling mill practice, the expanding inner flanges of a beam blank define an angle of 19.degree. with a normal to the longitudinal center line of the dogbone-shaped cross section. The inclined walls of the mold which bound the expanding casting passages must then intersect such a normal at the same angle. This presents a problem during continuous casting due to the fact that steel contracts as it cools and solidifies. Thus, when the steel adjacent to the walls of the mold solidifies, contraction of the steel causes the latter to come into frictional contact with the inclined walls of the mold. The friction increases the rate of wear of the inner surface of the mold so that the life of the mold is shortened. Furthermore, the friction adversely affects the surface quality of the beam blank. In addition, the friction increases the stress required to draw the beam blank out of the mold. The beam blank consists of a relatively large molten core and a relatively thin outer skin or shell upon leaving the mold, and the increased stress increases the likelihood of rupturing the skin. Rupture of the skin inside the mold is bad for the surface quality of the beam blank while rupture outside of the mold results in a "breakout", i.e., an escape of molten steel from the core of the beam blank.
The beam blank molds in use today also have another drawback associated with the fact that steel contracts as it cools and solidifies. Thus, as steel passes through a mold and is progressively cooled and solidified, the steel tends to pull farther and farther away from the walls of the mold thereby reducing heat transfer and decreasing the efficiency of the mold. To minimize reductions in heat transfer, it has become the practice to taper the casting passage so that this narrows in a direction from the inlet to the outlet of the mold. This at least partly compensates for contraction of the steel and allows relatively good heat transfer to be maintained. However, present beam blank molds cannot be effectively tapered.